1. Technical Field
This disclosure generally relates to correcting a phase error between in-phase and quadrature component signals.
2. Description of Related Art
Wireless communication systems often use quadrature phase generators for a variety of modulation and demodulation purposes. For example, it is often desirable to generate a quadrature phase local oscillator (LO) signal for either the down-conversion of a received signal or the up-conversion of a signal to be transmitted. In an ideal system, the quadrature LO signal includes a quadrature component (Q) that leads an in-phase component (I) in phase by exactly 90°. However, due to device mismatches, tolerances, layout parasitics, and other sources, signal paths for the I and Q signals may have different propagation delays. Consequently, there is a phase error component between the I and Q signals. Thus, quadrature LO generation circuits may have small errors from the perfect 90° phase quadrature. Any variation from the ideal quadrature phase difference of 90° at the outputs of the quadrature phase generator is regarded as a relative phase error between the I and Q signals. This phase error can reduce the image rejection and, if not corrected, may ultimately degrade transceiver performance.
There are several known ways of correcting phase error. For example, U.S. Pat. No. 6,016,422 (“'422”) uses a current controlled phase shifter in each path, thereby creating two independent paths, one for the in-phase signal and one for the quadrature signal. Because they are independent, they are subject to mismatches in layout parasitics and process parameters. Each phase shifter uses a fixed capacitor and a fixed resistor architecture. By changing the bias current in the “variable current controller” 809, the emitter resistance is changed allowing the “variable phase shift network 420” to “maintain phase quadrature over a 2:1 range of input frequencies.” However, in order to provide a consistent phase shift over a range of LO frequencies for a given control current, the resistor and capacitor may need to be scaled with frequency.
In U.S. Pat. No. 7,474,715 (“'715”), a variable capacitive load is applied to the I and Q LO signals to shift the phase. Similar to '422, the '715 patent may also need to be scaled with frequency in order to provide a consistent operation over frequency.
U.S. Pre-Grant Patent Publication 2012/0120992, U.S. Pat. Nos. 7,742,545, and 7,298,222 all use delay elements in each I and Q LO path to adjust the phase. These references are sensitive to frequency, because, for a given phase shift at a low frequency, a longer delay may need to be used than at a higher frequency, to obtain the same phase shift. It is with respect to these considerations and others that the present disclosure has been written.